Ink jet printers by which ink droplets are ejected from a nozzle onto a recording medium such as printing paper to form an image are provided with a common ink chamber and an ink-jet head including a plurality of individual ink passages from the common ink chamber to the nozzle. A passage portion of the ink-jet head is constituted by laminating a plurality of plate members formed with holes. One piece of a metal plate is used to form an intermediate plate on which a plate member is retained, and the intermediate plate is then cut off to manufacture the plate member. In forming the intermediate plate, etching process is given to the metal plate, thereby making one or a plurality of plate members retained on a framework. The plate member is retained on the framework by a bridge piece. In cutting out from the intermediate plate, a tool such as a punch is used to cut out the bridge piece, thereby cutting out the plate member from the intermediate plate (Patent Document 1).    [Patent Document 1] Japanese Published Unexamined Patent Application No. 2005-28641 (FIG. 7)